Conventionally, repositioning teeth is accomplished by wearing bands and braces, and using archwires, springs, and O-rings etc. The drawbacks of the conventional methods include poor appearance and comfort, and difficulty to maintain dental hygiene. In addition, a long term training is required before a clinician could practice the conventional methods. Furthermore, in conventional methods, a clinician needs to spend much time on adjusting the appliances during each patient visit, and this makes the treatment complicated. Compared with conventional appliances, an invisible orthodontic treatment does not require brackets and archwires, instead it uses a series of invisible appliances made of safe elastic transparent polymer materials. Therefore, the invisible orthodontic treatment is almost unnoticeable, and will not affect life quality. Meanwhile, since brackets and archwires are not required, clinical operation is greatly simplified, and much time and labor could be saved. Because of the above mentioned advantages, invisible orthodontic treatment is more and more popular.
Invisible appliances arise from the combination of computer aided method, rapid prototyping, and new materials. An invisible appliance is transparent, could be put on and taken off by the patient himself. Like conventional appliances, an invisible appliance also moves teeth by exerting proper and controlled forces on teeth. A practitioner may simulate the treatment on a computer, and may make an appliance using medical elastic transparent polymer materials for each stage of the treatment. In an invisible orthodontic treatment, a patient uses a series of invisible appliances in a predetermined order. When a patient wears an invisible appliance, he/her will feel load of forces on teeth, which will move the teeth toward an arrangement for which the appliance is designed. Having worn an appliance for a certain period of time, the patient may take off the current appliance, and put on a next appliance, and so on, until the teeth are moved from the original mal-aligned arrangement to an aligned arrangement gradually.
An invisible appliance may be made by manually modifying a positive plaster model of teeth, and then forming on the positive model the invisible appliance. However, this method has the drawbacks such as low precision, and low efficiency. An invisible appliance may also be made by first providing a digital data set representing a modified teeth arrangement, producing a positive model of the modified teeth arrangement by laser rapid prototyping, and forming on the positive model the invisible appliance. Conventional computer aided methods for manufacturing invisible appliances generate a plurality of intermediate teeth arrangements based on an original teeth arrangement and a final teeth arrangement using an interpolation algorithm. Once the final teeth arrangement is determined, the plurality of intermediate teeth arrangements are determined accordingly, therefore it is difficult to adjust or fine-tune the treatment between teeth during the treatment, and it is also difficult to set steps for corresponding operations on a same tooth separately. According to the above, a flexible method for designing and providing invisible appliances is needed.